We have further characterized a novel HTLV-1 like virus isolated from a baboon (designated BTLV). The envelope gene was cloned in an eukaryotic expression vector and it was found that the envelope gene directed the expression of a precursor protein of approximately 62 kda. The main objective for the past year was to elicit immune response to the envelope protein of that virus in mice. We also expressed a soluble form of the envelope protein and this construct was used for DNA immunization studies. Initially we compared intramuscular injection of plasmid DNA and DNA delivery mediated by the gene gun. For intramuscular injection, groups of mice (containing 5 in each group) were injected with 200 ug of DNA either alone or in combination with Lipofectin (Gibco BRL). The animals were subsequently boosted twice at four week intervals. Before the initiation of the experiment and before boosting, the animals were bled from the retro-orbital vein and the sera were used for the evaluation of immune response. The immune response was analyzed by performing ELISA, using a commercially available HTLV-1 detection ELISA kit (Virotech International Inc) or by using the 1621 cell line (developed from the baboon) as the antigen source. The ELISA results failed to show the presence of significant levels of antibody in the sera, subsequent to DNA immunization. The same sera were further used to immunoprecipitate envelope proteins synthesized in transfected cells. For that purpose, HeLa T4 cells were infected with vaccinia virus expressing T7 RNA polymerase and then transfected with plasmid DNA encoding the envelope protein. The cells were radiolabeled and the expressed proteins were immunoprecipitated with antibodies raised in miice. The proteins were resolved in SDS-PAGE and visualized using auto radiography. The results indicated that mice immunized with the DNA plasmid have developed antibodies which precipitated the labeled glycoprotein of 62 kda. Similar detection was observed when the antisera was used to detect the labeled soluble form of the envelope protein. Thus we have succeeded in eliciting antibody response using DNA immunization.